From bfc763df773ccfc10eb38a24caa111d0fcbc5493 Mon Sep 17 00:00:00 2001 From: Victoria Dye Date: Thu, 17 Mar 2022 15:55:35 +0000 Subject: [PATCH] unpack-trees: increment cache_bottom for sparse directories Correct tracking of the 'cache_bottom' for cases where sparse directories are present in the index. BACKGROUND ---------- The 'unpack_trees_options.cache_bottom' is a variable that tracks the in-progress "bottom" of the cache as 'unpack_trees()' iterates through the contents of the index. Most importantly, this value informs the sequential return values of 'next_cache_entry()' which, in the "diff cache" usage of 'unpack_callback()', are either unpacked as-is or are passed into the diff machinery. The 'cache_bottom' is intended to track the position of the first entry in the index that has not yet been diffed or unpacked. It is advanced in two main ways: either it is incremented when an index entry is marked as "used" (in 'mark_ce_used()'), indicating that it was unpacked or diffed, or when a directory is unpacked, in which case it is increased by an amount equaling the number of index entries inside that tree. In 17a1bb570b (unpack-trees: preserve cache_bottom, 2021-07-14), it was identified that sparse directories posed a problem to the above 'cache_bottom' advancement logic - because a sparse directory was both an index entry that could be "used" and a directory that can be unpacked, the 'cache_bottom' would be incremented too many times. To solve this problem, the 'mark_ce_used()' advancement of 'cache_bottom' was skipped for sparse directories. INCORRECT CACHE_BOTTOM TRACKING ------------------------------- Skipping the 'cache_bottom' advancement for sparse directories in 'mark_ce_used()' breaks down in two cases: 1. When the 'unpack_trees()' operation is *not* a "cache diff" (because the directory contents-based incrementing of 'cache_bottom' does not happen). 2. When a cache diff is performed with a pathspec (because 'unpack_index_entry()' will unpack a sparse directory not matched by the pathspec without performing the directory contents-based increment). The former luckily does not appear to affect 'git' behavior, likely because 'cache_bottom' is largely unused (non-"cache diff" 'unpack_trees()' uses 'find_index_entry()' - rather than 'next_cache_entry()' - to find the index entries to unpack). The latter, however, causes 'cache_bottom' to "lag behind" its intended position by an amount equal to the number of sparse directories unpacked so far with 'unpack_index_entry()'. If a repository is structured such that any sparse directories are ordered lexicographically *after* any pathspec-matching directories, though, this issue won't present any adverse behavior. This was the case with the 't1092-sparse-checkout-compatibility.sh' tests before the addition of the 'before/' sparse directory (ordered *before* the in-cone 'deep/' directory), therefore sidestepping the issue. Once the 'before/' directory was added, though, 'cache_bottom' began to lag behind its intended position, causing 'next_cache_entry()' to return index entries it had already processed and, ultimately, an incorrect diff. CORRECTING CACHE_BOTTOM ----------------------- The problems observed in 't1092' come from 'cache_bottom' lagging behind in cases where the cache tree-based advancement doesn't occur. To solve this, then, the fix in 17a1bb570b is "reversed"; rather than skipping 'cache_bottom' advancement in 'mark_ce_used()', we skip the directory contents-based advancement for sparse directories. Now, every index entry can be accounted for in 'cache_bottom': * if you're working with a single index entry, 'cache_bottom' is incremented in 'mark_ce_used()' * if you're working with a directory that contains index entries (but is not one itself), 'cache_bottom' is incremented by the number of entries in that directory. Finally, change the 'test_expect_failure' tests in 't1092' failing due to this bug back to 'test_expect_success'. Signed-off-by: Victoria Dye Signed-off-by: Junio C Hamano --- t/t1092-sparse-checkout-compatibility.sh | 6 +++--- unpack-trees.c | 16 ++++++++-------- 2 files changed, 11 insertions(+), 11 deletions(-) diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh index dcd7061fb3..236ab53028 100755 --- a/t/t1092-sparse-checkout-compatibility.sh +++ b/t/t1092-sparse-checkout-compatibility.sh @@ -340,7 +340,7 @@ test_expect_success 'deep changes during checkout' ' test_all_match git checkout base ' -test_expect_failure 'add outside sparse cone' ' +test_expect_success 'add outside sparse cone' ' init_repos && run_on_sparse mkdir folder1 && @@ -382,7 +382,7 @@ test_expect_success 'commit including unstaged changes' ' test_all_match git status --porcelain=v2 ' -test_expect_failure 'status/add: outside sparse cone' ' +test_expect_success 'status/add: outside sparse cone' ' init_repos && # folder1 is at HEAD, but outside the sparse cone @@ -593,7 +593,7 @@ test_expect_success 'checkout and reset (keep)' ' test_all_match test_must_fail git reset --keep deepest ' -test_expect_failure 'reset with pathspecs inside sparse definition' ' +test_expect_success 'reset with pathspecs inside sparse definition' ' init_repos && write_script edit-contents <<-\EOF && diff --git a/unpack-trees.c b/unpack-trees.c index 2763a029a1..b82c1a9705 100644 --- a/unpack-trees.c +++ b/unpack-trees.c @@ -595,13 +595,6 @@ static void mark_ce_used(struct cache_entry *ce, struct unpack_trees_options *o) { ce->ce_flags |= CE_UNPACKED; - /* - * If this is a sparse directory, don't advance cache_bottom. - * That will be advanced later using the cache-tree data. - */ - if (S_ISSPARSEDIR(ce->ce_mode)) - return; - if (o->cache_bottom < o->src_index->cache_nr && o->src_index->cache[o->cache_bottom] == ce) { int bottom = o->cache_bottom; @@ -1478,7 +1471,14 @@ static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, str * it does not do any look-ahead, so this is safe. */ if (matches) { - o->cache_bottom += matches; + /* + * Only increment the cache_bottom if the + * directory isn't a sparse directory index + * entry (if it is, it was already incremented) + * in 'mark_ce_used()' + */ + if (!src[0] || !S_ISSPARSEDIR(src[0]->ce_mode)) + o->cache_bottom += matches; return mask; } }